CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers his victory speech after being reelected for a second term at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers...

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CHICAGO, IL - NOVEMBER 06: U.S. Vice President Joe Biden and Dr. Jill Biden stand on stage after the victory speech by U.S. President Barack Obama on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney..

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. Vice President Joe Biden and Dr....

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Scott Olson, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Win McNamee, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama and U.S. Vice President Joe Biden embrace on stage after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama and U.S....

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama, U.S. Vice President Joe Biden and Dr. Jill Biden and family after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Jonathan Daniel, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama, U.S. Vice President Joe Biden and Dr. Jill Biden after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Scott Olson, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama and daughters Sasha and Malia after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer as they wait for Obama to appear on stage for his victory speech at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage after his victory speech at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: A supporter of U.S. President Barack Obama listens to his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: A supporter of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers his victory speech after being reelected for a second term at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama walks on stage with first lady Michelle Obama and daughters Sasha and Malia to deliver his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Win McNamee, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama walks on...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Win McNamee, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama waves to supporters after his victory speech at McCormick Place on election night November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama waves to...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage after his victory speech at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: Supporters cheer as U.S. President Barack Obama delivers his victory speech after being reelected for a second term at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters cheer as U.S. President...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama waves to supporters after his victory speech at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama waves to...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama waves to supporters after his victory speech at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama waves to...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Scott Olson, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama, U.S. Vice President Joe Biden and Dr. Jill Biden after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on stage with first lady Michelle Obama after his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama stands on...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers his victory speech after being reelected for a second term at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Scott Olson, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers...

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CHICAGO, IL - NOVEMBER 06: Supporters take photos as U.S. President Barack Obama delivers his victory speech after being reelected for a second term at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters take photos as U.S....

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers his victory speech after being reelected for a second term at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Jonathan Daniel, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama delivers...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Chip Somodevilla, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack Obama cheer after networks project Obama as reelected during the Obama Election Night watch party at McCormick Place November 6, 2012 in Chicago, Illinois. Networks project Obama has won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Scott Olson, Getty Images

CHICAGO, IL - NOVEMBER 06: Supporters of U.S. President Barack...

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CHICAGO, IL - NOVEMBER 06: The podium stands surrounded by confetti after U.S. President Barack Obama delivers his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney.

Photo: Scott Olson, Getty Images

CHICAGO, IL - NOVEMBER 06: The podium stands surrounded by...

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CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama walks on stage with first lady Michelle Obama and daughters Sasha and Malia to deliver his victory speech on election night at McCormick Place November 6, 2012 in Chicago, Illinois. Obama won reelection against Republican candidate, former Massachusetts Governor Mitt Romney. (Photo by Spencer Platt/Getty Images)

Photo: Spencer Platt, Getty Images

CHICAGO, IL - NOVEMBER 06: U.S. President Barack Obama walks on...

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Supporters of President Obama cheer for their candidate during the Obama Election Night watch party at McCormick Place in Chicago.

Photo: Chip Somodevilla, Getty Images

Supporters of President Obama cheer for their candidate during the...

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Romney supporters Rodney Paseka (left) and Gary Fox watch the returns during an election night watch party at the Venetian in Las Vegas.

Photo: David Becker, Getty Images

Romney supporters Rodney Paseka (left) and Gary Fox watch the...

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Spectators react to the results displayed on large TVs during the Romney campaign's election night event at the Boston Convention & Exhibition Center.

Photo: Alex Wong, Getty Images

Spectators react to the results displayed on large TVs during the...

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Supporters of President Obama cheer after networks project an Obama victory during the watch party at McCormick Place in Chicago, his hometown.

Photo: Chip Somodevilla, Getty Images

Supporters of President Obama cheer after networks project an Obama...

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BOSTON, MA - NOVEMBER 07: Republican presidential candidate, Mitt Romney, kisses his wife, Ann Romney, after conceding the presidency during Mitt Romney's campaign election night event at the Boston Convention & Exhibition Center on November 7, 2012 in Boston, Massachusetts. After voters went to the polls in the heavily contested presidential race, networks projected incumbent U.S. President Barack Obama has won re-election against Republican candidate, former Massachusetts Gov. Mitt Romney.

Photo: Matthew Cavanaugh, Getty Images

BOSTON, MA - NOVEMBER 07: Republican presidential candidate, Mitt...

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BOSTON, MA - NOVEMBER 07: Republican presidential candidate, Mitt Romney, wife, Ann Romney, wave to the crowd while walking off of the stage after conceding the presidency during Mitt Romney's campaign election night event at the Boston Convention & Exhibition Center on November 7, 2012 in Boston, Massachusetts. After voters went to the polls in the heavily contested presidential race, networks projected incumbent U.S. President Barack Obama has won re-election against Republican candidate, former Massachusetts Gov. Mitt Romney.

Photo: Alex Wong, Getty Images

BOSTON, MA - NOVEMBER 07: Republican presidential candidate, Mitt...

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BOSTON, MA - NOVEMBER 07: Republican presidential candidate, Mitt Romney, speaks at the podium as he concedes the presidency during Mitt Romney's campaign election night event at the Boston Convention & Exhibition Center on November 7, 2012 in Boston, Massachusetts. After voters went to the polls in the heavily contested presidential race, networks projected incumbent U.S. President Barack Obama has won re-election against Republican candidate, former Massachusetts Gov. Mitt Romney.

Photo: Justin Sullivan, Getty Images

BOSTON, MA - NOVEMBER 07: Republican presidential candidate, Mitt...

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Volunteer Clare Frew puts away a life-size cut out of presidential hopeful Mitt Romney as she prepares to close the Chatham County Republican Campaign office, Tuesday, Nov. 6, 2012, in Savannah, Ga. After a grinding presidential campaign, Americans are heading into polling places across the country.

Photo: Stephen Morton, Associated Press

Volunteer Clare Frew puts away a life-size cut out of presidential...

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At an election party at the Yerba Buena Center for the Arts, Reuben Telushkin, of Oakland reacts as President Barack Obama wins a second a second term on Tuesday Nov. 6, 2012 in San Francisco, Calif.

Photo: Mike Kepka, The Chronicle

At an election party at the Yerba Buena Center for the Arts, Reuben...

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At an election party at the Yerba Buena Center for the Arts, Reuben Telushkin, of Oakland reacts as President Barack Obama wins a second a second term on Tuesday Nov. 6, 2012 in San Francisco, Calif.

Photo: Mike Kepka, The Chronicle

At an election party at the Yerba Buena Center for the Arts, Reuben...

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At an election party at the Yerba Buena Center for the Arts, Reuben Telushkin, of Oakland reacts as President Barack Obama wins a second a second term on Tuesday Nov. 6, 2012 in San Francisco, Calif.

Photo: Mike Kepka, The Chronicle

At an election party at the Yerba Buena Center for the Arts, Reuben...

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At an election party at the Yerba Buena Center for the Arts, Kate Killbourne sends messages announcing that President Barack Obama wins a second a second term on Tuesday Nov. 6, 2012 in San Francisco, Calif.

Photo: Mike Kepka, The Chronicle

At an election party at the Yerba Buena Center for the Arts, Kate...

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At an election party at the Yerba Buena Center for the Arts, Jova Vargas of Oakland reacts as President Barack Obama wins a second a second term on Tuesday Nov. 6, 2012 in San Francisco, Calif.

A demographic tidal wave became a Democratic tidal wave as President Obama won a tight but decisive re-election victory Tuesday with the help of record-breaking support from Hispanic voters, massive turnout from African Americans and continuing enthusiasm from young Americans.

Although Republican nominee Mitt Romney won a larger share of the white vote than any presidential candidate since Ronald Reagan scored a landslide re-election victory in 1984, the former Massachusetts governor ended up a loser at the polls because of the racial, ethnic and generational changes that have altered the U.S. electoral landscape.

The portion of nonwhite voters in the electorate has tripled over the last four decades to 27 percent on Tuesday. The Democratic incumbent led among African Americans by 93 percent to 7 percent - the best performance by a Democrat since Lyndon Johnson in 1964.

Heavy African American turnout in Philadelphia, Detroit, Cleveland, Cincinnati and Miami changed the dynamic in four battleground states. In key swing states, Romney received just 1 percent of the African American vote in Florida and 3 percent in Ohio and Virginia.

Meanwhile, Latino voters, energized by tough Republican rhetoric on immigration, voted Democratic by 69 percent to 30 percent, tipping the balance of power in a string of states including Nevada, New Mexico and Iowa.

"Gov. Romney's shift to the right on the issue of immigration during the GOP primary season made it impossible for him to equal the number of Latino votes that George W. Bush received in 2000 and 2004," said Aaron Kall, director of debate at the University of Michigan. "Efforts by numerous states to curtail early voting and require photo identification seem to have motivated these groups to record turnout numbers."

In addition to minority voters, Obama's majority-making coalition included young voters, highly educated citizens and women.

For the first time in American history, Latinos made up 10 percent of the electorate, up from 9 percent in 2008. The overwhelming Hispanic support - and strong turnout - helped Obama win New Mexico and Iowa, and kept the race close in states such as Florida, Colorado and Virginia.

Shrinking GOP

In contrast to Obama's rainbow coalition, Romney's core supporters were older, evangelical and white. The Republican nominee did better among white voters than any Republican since Ronald Reagan in 1984, topping Obama by 20 points, 59 percent to 39 percent. Romney scored particularly well among older white men, white women who have not completed college and rural white males.

"We're seeing a Republican party whose support base continues to shrink," said Mark P. Jones, chairman of political science department at Rice University. "The GOP is going to have to address that support over the next few years, particularly as they approach the next presidential election."

With more than 80 percent of the votes counted nationwide, Obama had a lead of less than 1 percentage point in the popular vote - likely to grow when California's results are tallied. But Obama already had won enough states to clinch the 270 electoral votes needed to secure re-election.

In a gracious concession speech delivered shortly before 1 a.m. Eastern time, a subdued Romney called on disappointed Republicans to "earnestly pray" for Obama to succeed.

"This is a time of great challenge for America, and I pray that the president will be successful in guiding our nation," the Romney told a quiet crowd in Boston.

Obama's challenges include tackling a stubbornly high unemployment rate, a slow-growth recovery, record-breaking federal deficits and a burgeoning national debt. He also will preside over implementation of the controversial health-reform law approved by Congress in 2010 and due to take effect fully in 2014.

"While our road has been hard, while our journey has been long, we have picked ourselves up, we have fought our way back, and we know in our hearts that for the United States of America, the best is yet to come," Obama told supporters in his hometown of Chicago.

To succeed, Obama will need to break through partisan polarization that was reflected Tuesday at the polls. The president received the support of 92 percent of Democrats and 86 percent of liberals, while Romney was backed by 94 percent of Republicans and 83 percent of conservatives.

Year of the gap

Considering the deep divisions in the electorate, 2012 could easily be called "the year of the gap."

There was the gender gap. Women favored Obama, 54 percent to 44 percent, while men chose Romney by an almost identical margin, 53 percent to 45 percent. Mothers were more likely to support Obama (55 percent to 45 percent), while fathers sided with Romney (55 percent to 43 percent).

"Democrats effectively made the case that issues important to women, not just issues like abortion and reproductive rights but economic issues of equal pay and access to jobs, those issues resonated with women," said Ron Schurin, a political scientist at the University of Connecticut. "The Romney campaign seemed at times to be tone deaf on those issues. They tried to make a case, they just didn't do it effectively."

In addition to the gender gap, there was a yawning generation gap. Voters under the age of 30 were strongly pro-Obama, 59 percent to 37 percent, while voters 65 and older favored Romney by 57 percent to 43 percent. The Republican nominee benefited from an increase in turnout among seniors, up from 16 percent of the electorate in 2008 to 19 percent this year.

There also was a huge difference in voting patterns by place of residence. Urban voters sided with Obama, 61 percent to 37 percent, while Romney carried rural America by a similar margin, 59 percent to 39. Romney narrowly led Obama among suburban voters nationally because of big majorities in North Carolina, Georgia and Texas. But the GOP nominee was trounced in Pennsylvania and Virginia suburbs and performed below his expectations in Ohio, Colorado and Nevada suburbs.

One gap failed to materialize, however. Media reports of an "enthusiasm gap" among Democratic voting blocs turned out to be wrong.

Turnout among African Americans and young voters remained similar to 2008, while Latino turnout increased nationwide. The Hispanic vote was particularly significant in Nevada, where Latinos jumped from 15 percent of the electorate four years ago to 18 percent on Tuesday.

In the final week of the campaign, the incumbent benefited from widespread public praise for his response to Sandy, the powerful storm that slammed into the eastern seaboard a week before the election and temporarily froze partisan campaigning, with 79 percent of Americans rating the president's handling of the situation either "good" or "excellent," including more than four in five independents.